Gloy, gum and PVA : Practicality & Clear Advice.

Let us take a more practical; approach to these things.

 Gloy, gum arabic and PVA with plasticisers, all have similar qualities
which make them suitable for 'gum' printing.

The definition I gave of gum was from a reputable technical dictionary. The
additional ' or any substance with similar quailities' was from another
dictionary from the same stable. Dictionaries are practical guides, they are not
'authorities'.

As you say 'gum' itself is not a 'scientific' term. The implication of this
is that long technical discussions of its structure do not add much for the
purposes of the gum printer. In fact, i have been told by a significant
proportion of my recent students, capable and intelligent people. that such discussions
have led them to unsubscribe from this list.

A succinct explanation, free of jargon, does, however, help the student to
understand how the process works in practice. Long detailed explanations
replete with jargon do not help. Remember the principle that it is better to keep
things simple.

Terry

ll have to escape to
such a weak argument as "that is irrelevant to practice" or "pedantic
turn of mind" kind of nonesense. If thing's started with better
arguments, or better yet no such argument at all, we all spare
subsequent posts of rebuttal.

Terry

In a message dated 3/4/06 1:10:56 am, rs@silvergrain.org writes:

> From: TERRYAKING@aol.com
> Subject: Is PVA a 'Gum' ?
> Date: Sun, 02 Apr 2006 04:50:32 -0400 (EDT)
>
> > The reality is that PVA was developed after gum was defined as a
> > colloidal substance of plant origin which dissolve or wells in
> > water.
>
> Gum is not defined that way. First of all, "colloidal substance" is
> a semantically improper usage of the term colloidal. Colloid is a
> special case of dispersion and therefore at lest two phases must be
> involved. (Gum molecules can be one phase, of course, but unless there
> is another phase, there can't be a colloid.)
>
> Gum is not a scientific term. According to James BeMiller of Purdue
> University, "the term gum is applied to a variety of substances that
> produce sticky or slimy, viscous solutions or molecular dispersions or
> gels in an qppropriate solvent or swelling agent." It has nothing to
> do with what it is, how it works or what it's similar to.
>
> As I said above, PVA is not a definite compound, but its nomenclature
> has nothing to do with what people call gum.
>
>
> Finally, for those who want to endlessly argue the detaied chemistry
> of anything, I suggest not to post this kind of clearly incorrect and
> easily rebuttable arguments, especially if you'll have to escape to
> such a weak argument as "that is irrelevant to practice" or "pedantic
> turn of mind" kind of nonesense. If thing's started with better
> arguments, or better yet no such argument at all, we all spare
> subsequent posts of rebuttal.
>
Received on Mon Apr 3 02:28:01 2006